1. Field of the Invention
The present invention relates generally to a wavelength division multiplexed self-healing network, and more particularly to a bidirectional wavelength division multiplexed self-healing ring network, in which a central office and remote nodes are connected to one another using two optical fibers—add fiber and drop fiber. Optical signals are transmitted bidirectionally through the two optical fibers. And, the proposed ring network provides the self-healing function without the protection optical switch in the transmission path and doubles the transmission capacity in a normal operating state.
2. Description of the Prior Art
As the amount of the desired transmission traffic increases by the popularization of the Internet, the interest in optical networks that connect a central office to subscribers grows up.
The optical network should facilitate the provision of high-speed service to fulfill a demand for the high-speed service, and be economical to accommodate a large number of subscribers.
An optical network utilizing wavelength division multiplexing technology can transmit optical signals using various wavelengths regardless of transmission types and speeds, so communication networks can be effectively made to have a high-speed and a wide bandwidth.
In order to connect a central node to subscribers in the optical network, a remote node, which is placed near a group of subscribers, should be provided with a function of dropping and adding the signal assigned at each remote node.
Therefore, there is required a simple and economical wavelength division multiplexed optical network having add and drop functions.
The conventional wavelength division multiplexed access/Metro networks which connect a central office and remote nodes may be classified into three types: a unidirectional optical ring network using a single optical fiber, a unidirectional self-healing optical ring network using two optical fibers, and a mesh network.
In particular, an optical ring network has a relatively simple structure and can implement a self-healing function, so researches on the optical ring network have been actively carried out.
In a conventional unidirectional optical ring network, a central office and remote nodes are connected to one another by two optical fibers, one of the optical fibers transmits an optical signal in a normal operating state, and in case of a system failure, the ring network could be self-healed by detouring optical signals to the other optical fiber using an optical switch.
When optical signals are detoured through the other optical fiber in the conventional unidirectional optical ring network, the number of hops and a transmission distance of optical signals are increased in comparison with those in a normal state. Therefore, the quality of signals is deteriorated and expensive optical amplifiers may be employed to compensate for a loss due to the increased transmission distance.
Additionally, in the conventional optical ring network, signals are simultaneously added and dropped at each node, so the structure of the remote node is complicated and the requirements of the device are very strict. These features bring about increases of the system cost.